Data conversion failed from Curve to Loft Options

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Permalink Reply by Danny Boyes on March 30, 2014 at 2:37am

Hi fernando,

I have not got access to grasshopper today but from the error message above i guess you are trying to place curves into both inputs of [loft]. Only the upper input should take all of the curves you want to loft. The lower input is reserved for [loft options] a component dedicated to allowing you to change the types of lofts and how they are built.

Sorry i cannot help further with the offset failure.

Permalink Reply by David Rutten on March 30, 2014 at 3:26am

When you see an error that looks like:

Data conversion failed from X to Y

it means that you are providing data of type X to an input parameter of type Y and there is no automatic conversion defined between the two. A simple example would be if you plug Integer data into a Text parameter. It's perfectly possible to create a piece of text which represents the integer. I.e. the value 18 becomes the text "18".

It's also possible to convert a floating point number to text, although in that case the conversion is not lossless, as the text only shows a limited number of decimals, thus rounding the actual numeric value.

In your specific case here, you have connected a Curve parameter output with the Loft Options input. Loft options are about the type of loft, whether or not to rebuild/refit the resulting loft surface and -if so- what sort of tolerance to use.

If you look at the tooltips of the input parameter for the Loft component, you'll see that the first one takes all the section curves and the second one takes the options to be used to make the loft. You'll have to put all your curves into the first input:

This can be accomplished by holding SHIFT while making the second connection.

However this will generate a new problem. Loft operates on a list of curves, and for each list of curves you provide it will try to create a single loft. But if you merge the two curve streams, you'll sometimes get lists of 4 curves, this is probably not what you want.

At any rate, Loft is probably not what you want in the first place as an offsetted curve (especially curves with kinks) will result in incredibly messy lofts. I'd recommend Boundary Surface as an alternative, but that will generate trimmed surfaces, which may not be acceptable for you.

Now then, on to the Offset failure. Curve offsetting is a planar operation. By default, the plane in which Offset works is the world XY plane. Your curves are all perpendicular to the world XY plane, so that is already problematic. The fix would be easy (plug the curves also into the Offset P input), were it not that one of your section curves is wonky. This is probably either due to a bug in the Rhino Brep|Plane intersector or it's a problem with the input Brep. Either way, I could not get one of the curves to offset correctly, no matter what I tried.

In the end I solved it by using Loose Offset, which also means that the loft works much better because both the interior and the exterior curve have identical topology (see attached). Do note that Loose Offset does not guarantee an offset accurate to within document tolerance, it only moves the control-points.

--

David Rutten

david@mcneel.com

Attachments:

• LoftOffsetFail.gh, 1020 KB

Permalink Reply by Lukasz Domagala on June 30, 2017 at 7:09am

Hi David

I'm trying to script loft in python but I get type conversion error from text to loft options... My question is what type of data Loft Options is? 

list_crv=[m6,m5,m4,m2,m3,m1,m7]
list_crv=ghcomp.trees.FlattenTree(list_crv,{0})
l_o=ghcomp.trees.FlattenTree(ghcomp.LoftOptions(True,True,0,0,4),{0})
head_geo=ghcomp.Loft(list_crv,l_o)

Loft: input 2 Options. error: Data conversion failed from Text to Loft Options

Permalink Reply by Marios Tsiliakos on June 30, 2017 at 8:09am

Hi

I don't get this error. It also seems that the dictionary of the loft options described by the string is not deserialised properly to the correct options.

The default options seem to work as expected. Anything else doesn't.

Why aren't you using the rhinocommon method.?

kind regards,

M

Permalink Reply by Lukasz Domagala on June 30, 2017 at 8:24am

If I use

head_geo=rg.Brep.CreateFromLoftRefit(list_crv,0,0,rg.LoftType.Developable,True,0.001)

I get

1. Solution exception:expected IEnumerable[Curve], got list

For now I've used

head_geo=rs.AddLoftSrf(list_crv,None,None,4,0,0,True)

and it works

Any idea how to get rhinocommon method working?

Permalink Reply by Marios Tsiliakos on June 30, 2017 at 10:53am

You will have to import a .net List by importing System.Collections.Generic.

from System.Collections.Generic import List

ieList = List[rc.Geometry.Curve]()

for crv in list_crv:
ieList.Add(crv)

This should be working.

Best,

M

Permalink Reply by Lukasz Domagala on July 1, 2017 at 6:35am

Oh that's great, makes a lot of sense thank you. I'll try it on Monday

Permalink Reply by Lukasz Domagala on July 3, 2017 at 2:29am

That worked!

Thank you Marios